Heretofore, in fluid supply lines such as semiconductor manufacturing facilities and chemical industry facilities, piezoelectric element-driven valves and flow-rate control devices including piezoelectric element-driven valves have been widely used (for example, refer to patent document 1, patent document 2, patent document 3, patent document 4, patent document 5, patent document 6 and patent document 7).
FIG. 9 shows an example of a conventional piezoelectric element-driven valve 30 and a flow-rate control device including the piezoelectric element-driven valve 30.
That is, the flow-rate control device is composed of a piezoelectric element-driven valve 30, an inlet side block 32 fastened and fixed with a bolt (not illustrated) on the upstream side of a body 31 of the piezoelectric element-driven valve 30, and having formed therein an inlet side fluid channel 32a which is in communication with a fluid channel 31a of the body 31, a sealing gasket 33 interposed between the body 31 and the inlet side block 32, an outlet side block 34 fastened and fixed with a bolt (not illustrated) on the downstream side of the body 31 of the piezoelectric element-driven valve 30, and having formed therein an outlet side fluid channel 34a which is in communication with the fluid channel 31a of the body 31, a gasket type orifice 35 for controlling flow rate interposed between the body 31 and the outlet side block 34, a pressure sensor 36 arranged on the body 31 of the piezoelectric element-driven valve 30 and detecting the pressure on the upstream side of the gasket type orifice 35, a control unit 37 which controls the piezoelectric element-driven valve 30, and other components, and is so configured that the piezoelectric element-driven valve 30 is opened and closed to control the flow rate passing through the orifice while calculating the flow rate passing through the orifice by the pressure on the upstream side of the gasket type orifice 35.
Moreover, the piezoelectric element-driven valve 30 is formed as a normal close-type piezoelectric driven valve including the body 31 provided with the fluid channel 31a and a valve seat 31b, a valve element 38 (metal diaphragm) to be in contact with, and separated from, the valve seat 31b, a presser adapter 39 which presses the outer peripheral edge portion of the valve element 38 in an airtight manner toward the body 31 side, a split base 40 having a half-split structure which presses the presser adapter 39 toward the body 31, a base pressor 41 which fixes the presser adapter 39 and the split base 40 toward the body 31 side, an actuator box 42 supported ascendably and descendably by the base pressor 41, a diaphragm presser 43 which is inserted at the lower end of the actuator box 42 and is in contact with the valve element 38, an elastic body 44 which is interposed between the split base 40 and the actuator box 42 and downwardly presses and biases the actuator box 42, a piezoelectric actuator 46 which is accommodated in the actuator box 42 and which has a lower end side supported by the split base 40 via a lower receiver 45, an adjustment cap nut 49 which is threadably mounted on the upper end portion of the actuator box 42 and which positionably supports the upper end side of the piezoelectric actuator 46 via an upper receiver 47 and a thrust bearing 48, wherein extension of the piezoelectric actuator 46 due to application of a voltage causes the actuator box 42 to ascend while supported by the base pressor 41 against the elastic force of the elastic body 44 so as to, accordingly, cause the valve element 38 to be separated by the elastic force thereof from the valve seat 31b and the fluid channel 31a is opened, while the removal of voltage applied to the piezoelectric actuator 46 causes the piezoelectric actuator 46 to return to its original length dimension from an extended state and, the actuator box 42 is pressed down by the elastic force of the elastic body 44 to accordingly cause the valve element 38 to be pressed downward by the diaphragm presser 43 so as to come into contact with the valve seat 31b and, thereby, the fluid channel 31a is closed.
The piezoelectric actuator 46 using the piezoelectric element has the advantages of large thrust and good responsiveness and controllability, while it has the disadvantage that it has an extremely small amount of displacement of the piezoelectric element, so that it cannot have a greater stroke.
To solve the above-mentioned problems, a piezoelectric element-driven valve which is configured to transmit an amount of displacement of the piezoelectric element magnified by a displacement magnification mechanism to the valve rod having a lever structure has been developed (for example, refer to patent document 2 and patent document 6).
However, in the piezoelectric element-driven valve, a displacement magnification mechanism having a complicated structure needs to be incorporated between the piezoelectric actuator and valve rod, which creates another problems including troublesome assembly.
In contrast, in order to magnify the amount of displacement of the piezoelectric element and increase the stroke of the piezoelectric actuator, it is only necessary to stack two piezoelectric actuators vertically to configure a piezoelectric element-driven valve, but such a piezoelectric element-driven valve has not been developed so far.
Moreover, a piezoelectric element-driven valve in which the two piezoelectric actuators are simply stacked vertically is likely to have problems in wiring.
Although creating a longitudinal piezoelectric actuator achieves an increase in the stroke, in such types of piezoelectric actuators having stacked piezoelectric elements, the increase in the length of the piezoelectric elements may cause the entire piezoelectric elements to warp, which poses the problem that a highly accurate longitudinal piezoelectric actuator cannot be produced. Moreover, increasing the length of the piezoelectric element makes the same vulnerable to an external force from the horizontal direction (the direction which is perpendicular to the axis), and the piezoelectric element is disadvantageously likely to be damaged by the impact from the horizontal direction.